Measuring a subject's blood pressure information is extremely important in gaining an understanding of the subject's state of health. In recent years, attempts have been made to determine the cardiac stress or the level of arteriosclerosis not only by measuring a systolic blood pressure value and a diastolic blood pressure value, the usefulness of which as typical indices that contribute to the analysis of the risk of cardiovascular diseases such as stroke, heart failure, myocardial infarction, and the like has been widely acknowledged, but also, for example, by measuring the subject's pulse wave.
Blood pressure information measurement devices are intended to measure at least one of these types of blood pressure information, and are expected to be further used in fields such as early detection, prevention, and treatment of circulatory diseases. It should be noted that the blood pressure information includes a wide variety of types of circulatory information, such as systolic blood pressure values, diastolic blood pressure values, average blood pressure values, the pulse wave, the pulse, various indices indicating the level of arteriosclerosis, and the like.
Generally, a cuff for a blood pressure information measurement device (hereinafter also simply referred to as a “cuff”) is used to measure blood pressure information. Here, a “cuff” means a band- or ring-shaped structure that contains a compressing fluid bladder that can be attached to a part of a living body, and refers to those for use in measurement of blood pressure information, where an artery is compressed by inflating the compressing fluid bladder by injecting a fluid, such as a gas, a liquid, or the like, into the aforementioned compressing fluid bladder.
Usually, a blood pressure information measurement device is provided with a pressurization pump and an exhaust valve, which serve as a pressurization/depressurization mechanism for increasing/reducing the pressure of the compressing fluid bladder. Of these components, the pressurization pump is intended to pressurize the compressing fluid bladder and conventionally, a motor pump has been generally used as the pressurization pump.
In recent years, however, small-sized piezoelectric pumps suitable for suctioning and discharging a compressible fluid, such as air and the like, have come into actual use, and the use of such a piezoelectric pump as the pressurization pump of a blood pressure information measurement device has been considered.
The aforementioned piezoelectric pumps come in various types of configuration. In one type, an actuator is constituted by attaching a piezoelectric element to a vibrating sheet, and a diaphragm having a connecting hole though which a fluid passes is positioned opposite the actuator. By resonantly driving the piezoelectric element to thereby vibrate the vibrating sheet, the space between the actuator and the diaphragm functions as a pump chamber for enabling a pumping operation.
In a piezoelectric pump with this configuration, a fluid is introduced into the pump chamber from the suction side via the aforementioned connecting hole by displacement of the actuator toward the side opposite to where the diaphragm is located, and subsequently, the fluid is delivered to the discharge side from the pump chamber by displacement of the actuator toward the side where the diaphragm is located.
It should be noted that documents disclosing piezoelectric pumps with this configuration include, for example, International Publication No. 2011/145544 (Patent Literature 1).